scholarly journals Scanning transmission helium ion microscopy on carbon nanomembranes

2021 ◽  
Vol 12 ◽  
pp. 222-231
Author(s):  
Daniel Emmrich ◽  
Annalena Wolff ◽  
Nikolaus Meyerbröker ◽  
Jörg K N Lindner ◽  
André Beyer ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Dark Field ◽  
Acceptance Angle ◽  
Carbon Membranes ◽  
Thin Carbon ◽  
Helium Ion ◽  
Scanning Transmission ◽  
Contrast Mechanism ◽  
Ion Microscopy ◽  
And Performance

A dark-field scanning transmission ion microscopy detector was designed for the helium ion microscope. The detection principle is based on a secondary electron conversion holder with an exchangeable aperture strip allowing its acceptance angle to be tuned from 3 to 98 mrad. The contrast mechanism and performance were investigated using freestanding nanometer-thin carbon membranes. The results demonstrate that the detector can be optimized either for most efficient signal collection or for maximum image contrast. The designed setup allows for the imaging of thin low-density materials that otherwise provide little signal or contrast and for a clear end-point detection in the fabrication of nanopores. In addition, the detector is able to determine the thickness of membranes with sub-nanometer precision by quantitatively evaluating the image signal and comparing the results with Monte Carlo simulations. The thickness determined by the dark-field transmission detector is compared to X-ray photoelectron spectroscopy and energy-filtered transmission electron microscopy measurements.

First H+ Charge-Exchange Images in the Stim.

1976 ◽  
Vol 34 ◽  
pp. 504-505
Author(s):  
Wm. H. Escovitz ◽  
T. R. Fox ◽  
R. Levi-Setti
Keyword(s):  
Charge Exchange ◽  
Neutral Component ◽  
Channel Electron Multiplier ◽  
Electron Multiplier ◽  
Neutral Particles ◽  
Charged Beam ◽  
Scanning Transmission ◽  
Contrast Mechanism ◽  
Ion Microscopy ◽  
Beam Component

Charge exchange, the neutralization of ions by electron capture as the ions traverse matter, is a well-known phenomenon of atomic physics which is relevant to ion microscopy. In conventional transmission ion microscopes, the neutral component of the beam after it emerges from the specimen cannot be focused. The scanning transmission ion microscope (STIM) enables the detection of this signal to make images. Experiments with a low-resolution 55 kV STIM indicate that the charge-exchange signal provides a new contrast mechanism to detect extremely small amounts of matter. In an early version of charge-exchange detection (fig. 1), a permanent magnet installed between the specimen and the detector (a channel electron multiplier) sweeps the charged beam component away from the detector and allows only the neutrals to reach it. When the magnet is removed, both charged and neutral particles reach the detector.

scholarly journals Synthesis of nickel/gallium nanoalloys using a dual-source approach in 1-alkyl-3-methylimidazole ionic liquids

2019 ◽  
Vol 10 ◽  
pp. 1754-1767
Author(s):  
Ilka Simon ◽  
Julius Hornung ◽  
Juri Barthel ◽  
Jörg Thomas ◽  
Maik Finze ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Photoelectron Spectroscopy ◽  
Dark Field ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dual Source ◽  
Induced Decomposition

NiGa is a catalyst for the semihydrogenation of alkynes. Here we show the influence of different dispersion times before microwave-induced decomposition of the precursors on the phase purity, as well as the influence of the time of microwave-induced decomposition on the crystallinity of the NiGa nanoparticles. Microwave-induced co-decomposition of all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in the ionic liquid [BMIm][NTf2] selectively yields small intermetallic Ni/Ga nanocrystals of 5 ± 1 nm as derived from transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and supported by energy-dispersive X-ray spectrometry (EDX), selected-area energy diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). NiGa@[BMIm][NTf2] catalyze the semihydrogenation of 4-octyne to 4-octene with 100% selectivity towards (E)-4-octene over five runs, but with poor conversion values. IL-free, precipitated NiGa nanoparticles achieve conversion values of over 90% and selectivity of 100% towards alkene over three runs.

scholarly journals AP-XPS beamline, a platform for operando science at Pohang Accelerator Laboratory

2020 ◽  
Vol 27 (2) ◽  
pp. 507-514
Author(s):  
Geonhwa Kim ◽  
Youngseok Yu ◽  
Hojoon Lim ◽  
Beomgyun Jeong ◽  
Jouhahn Lee ◽  
...  
Keyword(s):  
High Resolution ◽  
Photoelectron Spectroscopy ◽  
Ambient Pressure ◽  
Experimental System ◽  
Photon Flux ◽  
Acceptance Angle ◽  
X Ray ◽  
Pohang Accelerator Laboratory ◽  
And Performance ◽  
X Ray Absorption

Beamline 8A (BL 8A) is an undulator-based soft X-ray beamline at Pohang Accelerator Laboratory. This beamline is aimed at high-resolution ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), soft X-ray absorption spectroscopy (soft-XAS) and scanning photoemission microscopy (SPEM) experiments. BL 8A has two branches, 8A1 SPEM and 8A2 AP-XPS, that share a plane undulator, the first mirror (M1) and the monochromator. The photon beam is switched between the two branches by changing the refocusing mirrors after the monochromator. The acceptance angle of M1 is kept glancing at 1.2°, and Pt is coated onto the mirrors to achieve high reflectance, which ensures a wide photon energy range (100–2000 eV) with high resolution at a photon flux of ∼1013 photons s−1. In this article, the main properties and performance of the beamline are reported, together with selected experiments performed on the new beamline and experimental system.

scholarly journals New Imaging modality for surface and sub-surface imaging using Scanning Transmission Helium Ion Microscopy

2021 ◽  
Vol 27 (S1) ◽  
pp. 770-772
Author(s):  
Saba Tabean ◽  
Santhana Eswara ◽  
Michael Mousley ◽  
Olivier De Castro ◽  
Jean-Nicolas Audinot ◽  
...  
Keyword(s):  
Imaging Modality ◽  
Surface Imaging ◽  
Helium Ion ◽  
Scanning Transmission ◽  
Ion Microscopy

Contamination at Low Temperature

1977 ◽  
Vol 35 ◽  
pp. 558-559 ◽  
Author(s):  
J. Wall ◽  
J. Bittner ◽  
J. Hainfeld
Keyword(s):  
Low Temperature ◽  
Heavy Atom ◽  
Carbon Film ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Transmission Electron ◽  
Surface Migration ◽  
Thin Carbon ◽  
Scanning Transmission ◽  
Atom Migration

Contamination of biological specimens has been a practical limitation for many years. It is especially noticeable in the dark field STEM (Scanning Transmission Electron Microscope) since contamination only occurs near the area irradiated by the beam and since we are most often observing very thin specimens (20 - 40 Å). Contamination can be greatly reduced by baking the specimen to 100°C in vacuum prior to observation, (1), but such heating may alter biological structures and cause heavy atom migration away from heavy atom staining sites.Since contamination results from surface migration (2), it might be eliminated by cooling the specimen to a sufficiently low temperature. The Brookhaven STEM (3).is equipped with a cold stage capable of attaining -170°C with less than 5 Å vibration. Contamination was observed as a function of temperature for a clean carbon film and for two biological specimens. The specimens were prepared on slotted Titanium grids covered by a holey carbon film with thin carbon (˜ 20 A) stretched across the holes.

Observing dislocations with ADF-STEM

1991 ◽  
Vol 49 ◽  
pp. 668-669
Author(s):  
Y. Huang ◽  
J. M. Cowley
Keyword(s):  
Material Science ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
High Angle ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Contrast Mechanism ◽  
Annular Dark Field ◽  
Annular Detector ◽  
Z Contrast

Scanning transmission electron microscopy (STEM) with a high angle annular detector has become a useful technique in material science. The atomic number sensitive contrast (Z-contrast) of the Annular Dark-Field (ADF) image is good for looking at the distribution of heavy elements in a relatively light substrate. In many cases the impurity distributions are substantially affected by the defects in the materials and their interaction with the impurities. Therefore it is also desirable to observe defects with ADF images. This is possible and has some advantages over normal STEM. We have studied the ADF imaging of dislocations, its contrast mechanism and visibility in the ADF image.

Diffraction Imaging in a He+ Ion Beam Scanning Transmission Microscope

2010 ◽  
Vol 16 (5) ◽  
pp. 599-603 ◽  
Author(s):  
John Notte IV ◽  
Raymond Hill ◽  
Sean M. McVey ◽  
Ranjan Ramachandra ◽  
Brendan Griffin ◽  
...  
Keyword(s):  
Ion Beam ◽  
Dark Field ◽  
Crystal Defects ◽  
Contrast Effects ◽  
Crystalline Materials ◽  
Helium Ion ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Diffraction Imaging ◽  
Good Agreement

AbstractThe scanning helium ion microscope has been used in transmission mode to investigate both the feasibility of this approach and the utility of the signal content and the image information available. Operating at 40 keV the penetration of the ion beam, and the imaging resolution achieved, in MgO crystals was found to be in good agreement with values predicted by Monte Carlo modeling. The bright-field and annular dark-field signals displayed the anticipated contrasts associated with beam absorption and scattering. In addition, the diffraction of the He ion beam within the sample gave rise to crystallographic contrast effects in the form of thickness fringes and dislocation images. Scanning transmission He ion microscopy thus achieves useful sample penetration and provides nanometer scale resolution, high contrast images of crystalline materials and crystal defects even at modest beam energies.

scholarly journals Imaging ultra thin layers with helium ion microscopy: Utilizing the channeling contrast mechanism

2012 ◽  
Vol 3 ◽  
pp. 507-512 ◽  
Author(s):  
Gregor Hlawacek ◽  
Vasilisa Veligura ◽  
Stefan Lorbek ◽  
Tijs F Mocking ◽  
Antony George ◽  
...  
Keyword(s):  
High Performance ◽  
High Surface ◽  
Thin Layers ◽  
Light Elements ◽  
Ion Channeling ◽  
Surface Sensitivity ◽  
Helium Ion ◽  
Contrast Mechanism ◽  
Assembled Monolayers ◽  
Ion Microscopy

Background: Helium ion microscopy is a new high-performance alternative to classical scanning electron microscopy. It provides superior resolution and high surface sensitivity by using secondary electrons. Results: We report on a new contrast mechanism that extends the high surface sensitivity that is usually achieved in secondary electron images, to backscattered helium images. We demonstrate how thin organic and inorganic layers as well as self-assembled monolayers can be visualized on heavier element substrates by changes in the backscatter yield. Thin layers of light elements on heavy substrates should have a negligible direct influence on backscatter yields. However, using simple geometric calculations of the opaque crystal fraction, the contrast that is observed in the images can be interpreted in terms of changes in the channeling probability. Conclusion: The suppression of ion channeling into crystalline matter by adsorbed thin films provides a new contrast mechanism for HIM. This dechanneling contrast is particularly well suited for the visualization of ultrathin layers of light elements on heavier substrates. Our results also highlight the importance of proper vacuum conditions for channeling-based experimental methods.

Mass Accuracy in the STEM

1988 ◽  
Vol 46 ◽  
pp. 236-237
Author(s):  
J. S. Wall
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Acceptance Angle ◽  
Mass Measurements ◽  
Contrast Transfer Function ◽  
Dark Field Imaging ◽  
Freeze Dried ◽  
Scanning Transmission ◽  
Digital Scanning ◽  
Large Acceptance

The scanning transmission electron microscope (STEM) has a number of features which make it ideal for quantitative studies: 1) large acceptance angle scintillator-photomultiplier detectors for low dose dark field imaging with linear electron detection, 2) simple contrast transfer function with no oscillations, 3) cold stage for zero contamination and reduced mass loss, 4) digital scanning for accurate magnification and positioning and 5) serial readout of several signals simultaneously for direct interfacing to a computer.For the past 10 years the Brookhaven STEM has been used for mass measurements on isolated individual molecules in freeze dried biological specimens. Interpretation of dark field STEM images is straightforward because of the clean background and linearity of the entire imaging process. Mass measurements provide a quantitative link to biochemical studies. Tobacco mosaic virus (TMV) usually is included along with the specimen of interest as a measure of the quality of the freeze drying and as a check on the microscope calibration, but is not necessary for absolute mass measurements.

Films That Wet Without Glow Discharge

1985 ◽  
Vol 43 ◽  
pp. 716-717
Author(s):  
J.S. Wall ◽  
J.F. Hainfeld ◽  
K.D. Chung
Keyword(s):  
Glow Discharge ◽  
Rock Salt ◽  
Unit Length ◽  
Carbon Film ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Specimen Preparation ◽  
Thin Carbon ◽  
Scanning Transmission ◽  
Thin Carbon Film

Mass measurements with the Scanning Transmission Electron Microscope (STEM) provide a direct link between biochemistry and the information in the dark field STEM image of an unstained biological specimen. Total mass of a complex mass of individual components, mass per unit length, mass per unit area, or change in mass distribution following biochemical treatment, are easily determined.Accuracy and preparation requirements have been described elsewhere. In the past year, we have made significant progress in specimen preparation, developing a “wet film” technique which eliminates the need for glow discharge treatment of grids. The method is similar to the Valentine technique but uses minute quantities of specimen. A thin carbon film is evaporated under UHV conditions onto freshly cleaved rock salt. The thin carbon is floated off the rock salt onto distilled water and a titanium grid with a thick, holey carbon film laid on top of it. After a few minutes, the grid is picked up from above by grasping its edge with a tweezer and turned over so that the adhering drop of water is facing upward.

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